Many vehicles are equipped with safety devices such as airbags and seat belt pretensioners to protect persons occupying various seats in the vehicle. If a seat is unoccupied or is occupied by a person of a particular size, it may not be necessary to activate a safety device associated with that seat. Furthermore, if a seat is occupied by a person of a particular size the manner in which a safety device is employed may be varied accordingly. One indicator of the seat occupant's size is the occupant's weight. In the case of an infant, the combined weight of the infant and an infant safety seat is useful as an indicator of occupant size. U.S. Pat. Nos. 5,232,243 and 5,494,311 teach a seat occupant sensor that is a piezoelectric film which is rigidly mounted to a substantially inflexible bottom portion of the seat. A plurality of sensing elements are arranged in rows and columns forming an array. U.S. Patent No. 5,454,591 teaches the use of this sensor to determine if a vehicle seat is occupied by an occupant weighing up to 40 pounds (about 18.2 kilograms) or more than 40 pounds (about 18.2 kilograms) and send an appropriate signal to a safety device control unit.
U.S. Pat. No. 5,474,327 teaches a seat occupant presence, weight and position sensor system wherein a plurality of sensors are located in the seat base just beneath the seat cover and some pressure is exerted on the sensors by the seat cover. The preferred sensors are mounted between polymer sheets and include a pair of conductive electrodes about 2.54 centimeters (1 inch) in diameter separated by carbon layers such that resistance between electrodes decreases as pressure increases.
U.S. Pat. No. 5,161,820 teaches a seat occupant sensor which is a switch, preferably a flat mat-like contact switch wherein two contact layers are separated by an intermediate, elastically deformable, electrically conductive layer. The contact switch is mechanically activated when the seat occupant compresses the intermediate layer and completes a conductive pathway for the switching circuit. The use of a simple physical contact switch or a condenser-type switch is also disclosed. However, the seat structure incorporating any of these switches is not shown in the drawings or described in the specification. The seat occupant sensor taught in this patent employs sensors located both in the seat and in the floor in front of the seat.
U.S. Pat. No. 4,678,058 teaches a vehicle seat switch assembly including a generally C-shaped spring located underneath the seat cushion. The end portions of the spring are displaced laterally when the spring is depressed when the seat is occupied. The lateral displacement of the spring ends pulls a switch plunger to close the switch.
U.S. Pat. Nos. 5,413,378 and 5,439,249 teach the use of an occupant weight sensor located in or on a structure that includes a seat cushion. The exact structure and operation of the occupant weight sensor is not disclosed in either of these patents. U.S. Pat. No. 5,466,001 teaches the use of sensors embedded in a seat cushion and seat back to sense occupant presence, but the structure of the sensors is not disclosed. U.S. Pat. No. 5,109,945 also teaches the use of a seat switch to detect a seat occupant but does not disclose the structure of the switch or the manner of incorporating the switch into the seat.
U.S. Pat. No. 5,481,078 teaches a seat occupant sensor wherein the seat rails pivot about their forward end against leaf springs designed to support the seat weight plus a known fraction of the occupant's weight so that the rear of the seat is raised when the seat is unoccupied. When the seat is occupied, the rear of the seat moves down and an electronic sensor detects seat position to provide a position signal.
U.S. Pat. Nos. 4,655,313; 4,361,741; and 4,509,614 also teach a vehicle seat switch used with a seat which pivots relative to the front of the seat cushion.
U.S. Pat. No. 5,120,980 teaches a foam seat cushion confining wire mesh electrical switch closing contacts. U.S. Pat. No. 5,164,709 teaches a seat occupant sensor which is a lateral-force-sensitive cable laid in a meandering pattern foamed into the seat cushion.
U.S. Pat. No. 4,806,713 teaches a seat-contact switch for generating a "seat occupied" signal when a seat suspension approaches a seat frame as a result of seat loading. An articulatable device is fastened on one end to the seat suspension and on the other end to the seat frame. U.S. Pat. No. 4,607,199 teaches the use of a seat switch in conjunction with a microprocessor to disable operation of a vehicle if the seat occupant is out of position for a given period of time. The switch structure and manner of incorporating the switch into the seat are not disclosed.
EP 0 728 636 A1 teaches the use of a switch sensor switch disposed in a seat base but does not disclose the switch structure and manner of incorporating the switch into the seat.
U.S. Pat. No. 4,633,237 teaches an occupant sensor for a hospital bed including a plurality of sensors defining interstices of a matrix of such sensors. The matrix is woven into a mat for placement on a bed in which a patient is confined.